This application is based on applications Nos. 2000-227639, 2000-258026 and 2000-396716 filed in Japan, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a photoelectric conversion device using numerous crystalline semiconductor particles, and to a manufacturing method thereof. The photoelectric conversion device according to this invention is utilized suitably in solar cells.
2. Description of the Related Art
Advent of a next-generation, low-cost solar cell that allows the quantity of silicon material to be small has been eagerly awaited.
Conventional photoelectric devices using crystalline semiconductor particles are shown in FIGS. 9-11.
FIG. 9 shows a structure disclosed in Japanese Patent Laid-Open Publication No. S61-124179. In this photoelectric conversion device, a first aluminum foil 10 is provided with openings 10a into which silicon balls 2 having n-type surface portions 9 on the surfaces of p-type balls are inserted. The n-type surface portions 9 of the silicone balls 2 projecting from the rear surface of the first aluminum foil 10 are then removed. An oxide layer 3 is formed on the rear surface side of the first aluminum foil 10, and then a second aluminum foil 8 is formed such that it eliminates the oxide layer 3 at parts covering the silicon particles so as to be joined to the silicon particles 2.
FIG. 10 shows a structure disclosed in Japanese Patent No. 2641800. In this photoelectric conversion device, a low-melting-point metal layer 11 such as a tin layer is formed on a substrate 1. First conductivity-type crystalline semiconductor particles 2 are deposited on the low-melting-point metal layer 11, on which a second conductivity-type amorphous semiconductor layer 7 is formed with an insulating layer 3 interposed between it and the low-melting-point metal layer 11.
FIG. 11 shows a structure in Japanese Patent Publication No. H8-34177 disclosing a method in which a high-melting-point metal layer 12, a low-melting-point metal layer 11, and semiconductor microcrystalline particles 13 are deposited on a substrate 1, and the semiconductor microcrystalline particles 13 are fused, saturated and gradually cooled so that the semiconductor is grown by liquid phase epitaxial growth, thereby transforming the semiconductor microcrystalline particles 13 into a polycrystalline thin film. In FIG. 11, the numeral 14 denotes the opposite conductivity-type polycrystalline or amorphous semiconductor layer, and the numeral 6 denotes a transparent conductive layer.
However, according to the photoelectric conversion device shown in FIG. 9, the first aluminum foil 10 needs to be formed with openings into which the silicon balls 2 are pressed so as to join the n-layer 9 of the silicon balls 2 to the aluminum foil 10. Therefore, evenness is required for the particle sizes of the silicon balls 2, which causes high manufacturing costs.
In addition, in the photoelectric conversion device shown in FIG. 10, since the insulator 3 is formed after securing the crystalline semiconductor particles 2 on the low-melting-point metal layer 11, the insulator 3 is formed not only on the low-melting-point metal layer 11 but also on the crystalline semiconductor particles 2. Accordingly, it is necessary to remove the insulator 3 on the crystalline semiconductor particles 2 before forming the amorphous semiconductor layer 7. The number of processes therefore increases necessitating stricter management of the cleaning process and the manufacturing environment, which leads to a high-cost production.
Also, the photoelectric conversion device shown in FIG. 11 has problems that the low melting-point metal 11 mixes into the first conductivity-type liquid phase epitaxial polycrystalline layer 13, thereby deteriorating the performance, and that the absence of insulator causes leakage to occur between the layer and the lower electrode 12.
A primary object of the present invention is to provide a photoelectric conversion device having good conversion efficiency that can be manufactured at a low cost, and a manufacturing method thereof.
A method of manufacturing a photoelectric conversion device according to the present invention comprises the steps of: applying numerous glass particles having a particle size before baking being 5 to 25% of that of crystalline semiconductor particles to a substrate having an electrode of one side; depositing the crystalline semiconductor particles on the layer of the glass particles; pressing the crystalline semiconductor particles against the substrate; and subjecting them to baking, whereby manufacturing a photoelectric conversion device in which the crystalline semiconductor particles and the substrate are in contact together as well as an insulator has been interposed among the crystalline semiconductor particles (claim 1).
According to this method of manufacturing a photoelectric conversion device, since the glass particles are in the above-mentioned range in particle size, it is possible to apply the insulator to the substrate in a relatively uniform manner. In addition, when the crystalline semiconductor particles are pressed against the substrate, the glass particles are ejected from between the substrate and the semiconductor particles such that the glass particles slide into beside the semiconductor particles, so that an ohmic contact can be formed between the substrate and the semiconductor particles.
A photoelectric conversion device according to the present invention comprises: a substrate having an electrode of one side; numerous crystalline semiconductor particles deposited on the substrate; and an insulator interposed among the crystalline semiconductor particles, wherein the insulator is formed by baking a layer of glass particles that has been applied to the substrate, the insulator comprising a filler having a particle size being 5 to 25% of that of the crystalline semiconductor particles (claim 4).
According to this photoelectric conversion device, even when the glass particles are small in particle size, as long as the filler is in the above-mentioned range in particle size, the glass particles are ejected along with the filler from between the substrate and the silicon particles to be located beside the silicon particles when the silicon particles are pressed against the substrate.
Another method of manufacturing a photoelectric conversion device according to the present invention comprises the steps of: applying numerous glass particles including a filler dispersed therein to a substrate having an electrode of one side; depositing crystalline semiconductor particles on the layer of the glass particles; pressing the crystalline semiconductor particles against the substrate; and subjecting them to baking, whereby manufacturing a photoelectric conversion device in which the crystalline semiconductor particles and the substrate are in contact together as well as an insulator has been interposed among the crystalline semiconductor particles (claim 7).
According to this method of manufacturing a photoelectric conversion device, the filler particles that have been dispersed within the glass particles are dispersed homogeneously within the insulator layer by the melting of the glass particles at the baking temperature. Accordingly, unevenness in thermal expansion coefficient in the insulator layer is lessened and generation of cracks caused by stress is prevented from occurring in the semiconductor particles.
In addition, another photoelectric conversion device according to the present invention comprises: a substrate having an electrode of one side; numerous crystalline semiconductor particles deposited on the substrate; and an insulator interposed among the crystalline semiconductor particles, wherein the glass insulator comprises plural materials, and has a thermal expansion coefficient in the range of 30xc3x9710xe2x88x927/xc2x0C. to 60xc3x9710xe2x88x927/xc2x0C., and a softening point of 500xc2x0 C. or below (claim 14).
According to this photoelectric conversion device, numerous crystalline semiconductor particles are deposited on a substrate and heated so that both of them are joined together by alloy portions where both of them are fused, and an insulator is interposed among the numerous crystalline semiconductor particles. The structure being as above, this invention allows for formation of a good insulator in which generation of defects such as cracks and voids is prevented, thereby providing a photoelectric conversion device with high reliability.
As has been discussed so far, by the method of manufacturing a photoelectric conversion device according to the present invention or by the photoelectric conversion device according to the present invention, it is possible to form a good insulator while contacting a substrate and semiconductor particles together. That is, it is not necessary to bore holes in the electrodes, and single conductivity-type semiconductor particles with low particle size accuracy can be used, as well as light incident on areas where the semiconductor particles are not present can be utilized. Furthermore, the insulator above can prevent current leaks from occurring between the semiconductor layer and the electrode of the substrate.
Accordingly, it is possible to achieve high conversion efficiency at a lower cost.
Furthermore, owing to the flexibility in shape, a photoelectric conversion device having little dependence on the light incidence angle can be provided by this invention.
Structural details of the present invention are hereinafter described referring to the accompanying drawings.